1. Field of the Invention
The present invention relates to amorphous metal alloy compositions, and, in particular, to Fe-system amorphous metal alloy strips containing iron, silicon, boron , carbon and phosphorus, having enhanced AC magnetic properties for use in electric power transformer cores and high frequency transformer cores.
2. Description of the Prior Art
The need has been recognized for processes such as processes, melt-spin single roll processes or twin roll processes etc, which permit manufacture of finished or semifinished products such as wire,ribbon or sheet directly from the molten metal. These processes involve rapid quenching of a jet of molten metal from an orifice directed against a moving chill surface, such as the inside or outside of a rotating roll. It also has become apparent that certain amorphous metal strip materials may posses magnetic and physical properties that enhance their usefulness as materials in various applications by proper selection of the alloy compositions.
Amorphous metal alloy strips shows great promise as industrial materials in various uses because of their superior characteristics. Alloy compositions for strip material for use in electric power transformers and high frequency transformers having a Fe--Si--B system alloy is especially well established because it shows low core loss, high magnetic flux density and high permeability.
It is known, however, that when such a metal alloy strip is continuosly cast, a raw material whose content of impurities is extremely limited is used to avoid increasing core loss. Electrolytic iron is used as a raw material. The impurity elements whose concentration should be restricted are,for example phosphorus and sulfur. Japanese Unexamined Patent Publication No.59-16947 discloses amorphous metal alloy compositions consisting essentially of 86 to 95% of Fe, 0-11% of Si, 2-4% of B and 0-1.5% of C, by weight %, which converted to an atomic percentages are 65.9-85.4% of Fe, 0-18.3% of Si, 8.3-17.6% of B and 0-6.1% of C respectively, and further containing not more than 0.015 wt % of P and not more than 0.02 wt % of S, and describes that P is an element which increases core loss and S is an element increasing brittleness. Relating to the process conditions only disclosed in this patent publication, there is no specific description other than a quenching rate of more than 10.sup.5 .about.10.sup.6 .degree. C./sec and the strip having a thickness of about 30 .mu.m in the Examples.
Japanese Unexamined Patent Publication No.57-137451 discloses amorphous metal alloy containing a maximum allowable amount of impurities, such as not more than 0.008% of P, not more than 0.12% of Mn and not more than 0.02% of S , by atomic percentages. This amorphous metal alloy composition consists essentially of 78.5%-80% Fe, 5-10% Si and 13-16% B, by atomic percentages. Therefore, the amount of the above mentioned P, Mn and S, converted to weight %, are not more than 0.053% of P, not more than 0.14% of Mn and not more than 0.0136% of S, respectively. These impurities such as P, Mn and S, as disclosed, are harmful elements which increase core loss.
Composition design of amorphous metal alloys containing a low amount of harmful impurities,i.e. P, Mn and S has been carried out to decrease core loss. However, the following prior art shows that P can be used advantageously.
Japanese Unexamined Patent Publication No.57-185957 discloses an amorphous metal alloy strip containing 1 to 10 atomic % of P in a Fe--Si--B--C--P system alloy to reduce core loss and improve magnetic flux density. However, this patent publication also discloses as an additional condition a content of at least one element selected from Al, Sn, Ge, Ti, Zr, Nb, V, Mo or W in an amount of not more than 5 atomic %.
Japanese Patent Publication No.58-42261 discloses amorphous metal alloy strip containing not less than 5 atomic % of P in a Fe--Cr--C--P system alloy and Fe--Cr--B--P system alloy for improving the tensile strength and heat resistance.
Japanese Unexamined Patent Publication No.51-73920 discloses amorphous metal alloy strip containing only 7 to 35 atomic % of P in a Fe--Si--B--C--P system alloy for increasing magnetic flux density.
As evident from the above, no amorphous metal alloy strip, or its production process, has been found which contains only P in a Fe--Si--B--C system alloy to decrease core loss. Furthermore, it is difficult to use the iron materials produced by an ordinary steel making process from iron ore as a material for production of an amorphous metal alloy strip, because the allowable range of impurities is very narrow in for production of a Fe--Si--B--C system amorphous metal alloy strip, because an ordinary steel material contains an amount of impurities exceeding the allowable range.
It is possible to use a high purity material, such as electrolytic iron, because of its reduced range of impurities. On the other hand, use of expensive high purity raw material increases the production cost of the amorphous metal alloy strip. The resultant characteristics considerably vary from lot to lot, and lead to a lower a yield ratio and to increased cost. There has long been a demand to lower the production cost of amorphopus metal alloy strip for its widespread use as an industrial material